1. Field of the Invention
This invention relates to compositions and processes for cleaning engineering plastic surfaces. Surfaces that can be effectively cleaned according to this invention include, but are not limited to, polyester sheet molding compound ("SMC"); poly(vinyl chloride) ("PVC") homopolymers and copolymers; polyurethane and polyurea plastics such as those made commercially by injection molding; terpolymers of acrylonitrile, butadiene, and styrene ("ABS"); poly{phenylene oxide} ("PPO") and copolymers of "phenylene oxide" with other materials such as polyamides; polycarbonate ("PCO") polymers and copolymers; and thermoplastic polyolefins ("TPO"). The invention is particularly suited to cleaning plastics, more particularly SMC, that contain solid filler materials, especially those that are chemically alkaline, such as calcium carbonate. Common commercially available types of such SMC materials include PHASE ALPHA.TM. from Ashland Chemical Co., SL 1223.TM. from Eagle Picher Co., Type 7113.TM. from Gencorp, and RI 9486.TM. from Rockwell International, Inc.
The compositions of the invention are substantially or entirely free from phosphate and can be substantially or entirely free from volatile organic solvents as well, and are therefore less polluting than the now common commercial acidic cleaners for plastics.
2. Statement of Related Art
Numerous compositions and processes for cleaning plastic surfaces are currently known in the art. Most of them include acid, surfactant(s), and phosphates. In some locations, however, phosphates are forbidden or severely limited to avoid potential pollution and eutrophication of bodies of water that receive discharges of industrial waste water. Thus, compositions that contain little or no phosphate but are still effective cleaners have been sought.
U.S. Pat. No. 4,895,658 according to an abstract thereof teaches compositions containing a weak organic acid and an acrylic polymer for cleaning semipermeable membranes, particularly cellulose acetate and triacetate, polyamide, and polysulfone membranes. Preferred weak acids are citric, malic, sulfamic, and mixtures of these.
Hungarian published accepted specification T046736 according to an abstract thereof teaches compositions including citric acid and a partially hydrogenated caprolactam oligomer as cleaning agents for ceramic cladding materials.
Published European patent application 0 213 500 according to an abstract thereof teaches liquid detergent compositions containing surfactants, an agent to retard redeposition of soil, and optionally a water soluble sequestrant builder that may be or include citrates.
Published Japanese application 62-004792 according to an abstract thereof teaches a cleaner for removing mold that comprises peroxides, phosphoric acid or phosphate salts, divalent cations, and lower carboxylic acids or salts thereof. Citric acid and citrates may constitute the latter ingredient.
Published Japanese application 61-276899 according to an abstract thereof teaches a cleaner for fiber reinforced plastic moldings. The cleaner is improved by adding to the "usual" ingredients, such as surfactant(s) and organic solvent(s), a dicarboxylic and/or hydroxycarboxylic acid, which may be citric acid.
Published Japanese application 61-118499 according to an abstract thereof teaches a spray cleaning composition for plastic articles. The composition comprises water insoluble inorganic powder and conventional surfactants and may also contain builders, defoaming agents, chelating agent, and solvent. Citric acid is taught as an example of a chelating agent.
Published East German patent application 208177 according to an abstract thereof teaches a composition containing citric acid, phosphate salt, wetting agent, and corrosion inhibitor as useful for cleaning metal or plastic surfaces from corrosive etching solutions or their reaction products.
Published Japanese application 57-105494 according to an abstract thereof teaches a detergent composition containing polyoxyethylene alkyl ether (a nonionic surfactant) and sodium citrate as its main components and optionally containing additional components. This composition is recommended for cleaning plastic sheets used in horticulture.
Published Japanese application 53-018606 according to an abstract thereof teaches a composition for cleaning metal, plastic, or glass. The necessary ingredients of the composition include lithium salts of an acidic partial ester of sulfuric acid, of a sulfonic acid, or of an alkanolamine. Citric acid is shown as an optional ingredient.
Patent publication 536221 from the U.S.S.R. according to an abstract thereof teaches an emulsifier for cleaning metal surfaces. The emulsifier contains oxyethylated alcohol; mono-, di-, or tri-ethylamino carbonate; disodium mono-, di-, or tri-ethylamino ethylenediaminetetraacetate or sodium tripolyphosphate; sodium citrate; and water.
British published patent application 1 487 715 according to an abstract thereof teaches a "universal" acidic cleaning product containing phosphoric acid, citric acid, and esters of phosphoric acid together with alkylaminopoly glycol ether surfactant and sufficient basic constituents to produce a pH of about 2.